Taxman, I would start by determining where the problem is: in the unit or the temperature sensor. Do this by testing your 997 unit on another Humminbird transducer that has the built-in temperature (does not matter which model it is). You can also test another Humminbird unit on your boat’s 997 connections but be sure to only connect the power and transducer for this testing. Most of the time the problem is in the built-in temperature sensor in the transducer. There is no fixing these as the entire transducer has to be replaced. Keep in mind that if you are using a multiple transducer system that the transducer splitter cable could be at fault as well so you would need to plug each transducer directly into the unit thus eliminating or incriminating the transducer splitter cable as the problem (or not).